1. Field of the Invention
This invention relates to injection devices for the dispensation of medicaments and, more particularly, to such devices that are self-dispensing continuously, periodically or at different intervals.
2. Description of the Prior Art
It is known to use injection needles for continuous or periodic subcutaneous or intramuscular introduction of aqueous, oil-based or other liquid-based medicaments into body tissue. These injection needles can be connected to a mechanical or automatic dosage device by means of a tube of material which is tissue compatible and is substantially inert with respect to the medicament solution.
For the treatment of certain illnesses such as Parkinson's disease, among others, a continuous or periodic supply of medicament is desired because, in this manner, uniformity of dispensation of the active ingredient or ingredients of the medicament solution may be attained in the patient's body. In order to allow the patient both freedom of movement and also the avoidance of the inconvenience of stationary treatment as well as mistakes in introduction, it is conventional to use an electronic dosage pump which is carried on or affixed to the body. The pump releases the medicament via a tubular duct through an injection cannula fixed in the subcutaneous or muscle tissue, but this can create a problem. For example, medicament concentrations at the entry point into the body tissue are higher than may be needed. The increased medicament concentrations arising at the injection spot can, depending on the chemistry of the medicament as well as its concentration, lead to local irritation and inflammatory types of conditions which in extreme cases can make it necessary to end the beneficial therapy.
U.S. Pat. No. 4,159,720 describes an apparatus which introduces the medicament solution into the body from a reservoir fastened on the skin through a wick of silk or medical sewing material. This method has the disadvantage that the dosage rate is predetermined by the wick surface area and its absorption characteristics. Therefore, it is unlikely that a prescribed dosage rate over the course of the day can be realized. Furthermore, tissue compatibility of the wick material can be a problem in certain cases. To the same effect is Australian Patent No. 253,426 which is directed to a syringe having cannulae extending in opposed directions from a hub. Again, the concentration problem and resultant irritation are not obviated.
In Federal Republic of Germany Laid Open Patent Application No. DE-OS 30 35 009, an injection head is disclosed. It is provided with supports for receiving injection needles. This is, however, envisaged as part of an injection tip for heat spot formation. Because of the size and shape and the constructional details of the injection head and the support for receiving the injection tip, this device is not suitable to be worn on the body for prolonged periods of time after fixing in the desired injection position.
In French Patent No. 11 42 769, an injection needle is described which has lateral openings so that the medicament to be injected is divided in the tissue along the needle. In spite of the division into different effective depths, it does not address the problem of undesired concentrations at the entry point or the need for spreading the medicament laterally along the surface of the patient's body.
French Patent No. 11 33 709 describes an apparatus for reflex therapy which has a box-like reservoir for a medicament, whereby a plurality of parallel injection needles extend from the base of the reservoir and are connected with the latter via capillaries so that only drops are introduced onto the skin area. Again, this apparatus is not suitable for fixing on the body for anything but the briefest periods.
Thus, this invention directly addresses the problem of providing an injection device for scheduled self-injections of medication which can be easily fixed on the body and which obviates the concentration centers of prior art devices.